‘awesomium_process.exe’

Left-clicking on the ground is the most reliable way to deselect all targets.

ESC deselects any selected targets, but if nothing is selected you will bring up your menu (can be annoying mid-combat).

There is also a key binding to target the nearest ally, which will select yourself if no other allies are around. This is useful if you are having trouble finding a patch of ground to click on. This key is not assigned by default, so look for "Nearest Ally" under Targeting in Options->Controls.

You can also select the next closest target using TAB, in case you do actually want to direct your spells towards a different enemy then the one you current have selected. Then again, a left-click on the target works more reliably if multiple targets are in view.

There is also a Guild Wars 2 printable keyboard layout to help you visualize the default key bindings.

"Bonus Experience - When you kill an enemy in the world, you might see 5 xp + 2 xp pop up . What this means is you’ll gain bonus experience depending on how long an enemy has been alive in the world, which gives you even more incentive to explore."

Enemies that have been alive (bear with me, that's a huge article. Somewhere halfway through) for a longer amount of time than other mobs give bonus experience based on the amount of time they've been around. This is to discourage grinding in one place.

Note: The amount of XP you receive is also respective of your level.